Copper(II) complexes with N-(2-carboxyethyl)anthranilic acid H2CEAnt. Synthesis and crystal structure of [Cu(CEAnt)(H2O)] ⋅ H2O

Abstract

Protolytic equilibria and complexation of N-(2-carboxyethyl)anthranilic acid (H2CEAnt) with copper(II) ions in aqueous solutions were studied by UV spectroscopy and pH potentiometry. The H2CEAnt compound has no zwitterionic structure, and the protons are localized on the carboxy groups. The acid ionization constants of H3CEAnt+ (T = 25 °C, I = 0.1 M KNO3) are pK0 = 1.3±0.2 (=NH2+), pK1 = 3.88±0.02 (Alk-COOH), and pK2 = 5.28±0.02 (Ar-COOH). The model of complexation of H2CEAnt with copper(II) ions involves two deprotonated complexes [Cu(CEAnt)] and [Cu(CEAnt)2]2− (logβ = 6.31±0.04 and 8.0±0.2, respectively). The [Cu(CEAnt)(H2O)]⋅H2O complex was synthesized by the reaction of H2CEAnt with (CuOH)2CO3, and its structure was established by X-ray diffraction. The coordination polyhedron of Cu is intermediate between the tetragonal pyramid and trigonal bipyramid. The CEAnt2− ligand serves as a tetradentate chelating bridging ligand (Cu-O, 1.944(3) and 1.950(3) A; Cu-O', 2.195(4) A; Cu-N, 2.016(5) A), and the fifth position of the polyhedron is occupied by a water molecule (Cu-Ow, 1.976(4) A).